Technical Field

The present invention relates to a plant for the recovery of white slag resulting from iron and steel processes, particularly in the refining phases of the liquid steel.

Background Art

As is well known, in the refining processes of steel in ladles (deoxidation, desulphurization and final definition of the analytical composition), a certain quantity of slag is always generated (so-called“white”) due to the chemical interactions between the bath with the non-metallic charge (lime, calcium aluminates, fluxes), the metal additives (deoxidants, ferroalloys, etc. ...) and the refractories.

Applicable regulations define white slag as special waste and this must therefore be disposed of, with consequent increases in production costs and environmental impact.

To overcome these problems, in recent years there has been a significant increase in proposals aimed at the recovery of white slag with the aim of achieving significant benefits both from the production point of view, and from the environmental point of view thanks to less disposal in landfills, less exploitation of quarries to obtain limestone to be sent for firing for the preparation of lime and high savings in terms of carbon dioxide emissions.

Known technologies aim to recover, preferably in a furnace, the white slag that forms in the ladle during the final stages of production of the liquid steel.

White slag is a material still rich in lime which, following adapt and suitable preparation, can be directly reused within the same production cycle as a scorifier to partially replace the raw materials (circular economy). The intended aim is, therefore, to reuse a material with a high environmental impact instead of“throwing it away” as special waste.

The technologies known to date and which are briefly described below, have in common problems such as to limit or even prevent their development and industrial application. In patent literature, there are various types of treatments for the recovery of white slag, some of which apply static type cooling, where the material is left to cool inside a relative chamber until it is completely pulverized. As can be easily appreciated, this type of treatment requires times extending over several days. Another known type of treatment envisages cooling inside reactors of the rotary type, where the material is inserted into a rotating dram externally cooled by water. A solution of this type is, for example, that described in EP 3 247 811, wherein a method is illustrated for the recovery of white slag by means of controlled cooling inside a rotating cylinder and screening thanks to the selection and separation of fragments in a continuous cycle with rotation of the cylinder in controlled atmosphere. The rotating cylinder comprises a first portion for controlled cooling in order to lead to a process of withering of the white slag, with consequent detachment of fragments and dusts, and a second portion, placed in cascade to the first, wherein the selection and separation is performed of fragments and dusts of the white slag having a size below a predetermined size.

Another separation solution is described in EP 3 323 898, which illustrates a rotating drum adapted to receive the white slag inside it. The drum comprises a cooling segment to induce a process of withering of the white slag, and a screening segment, placed in cascade to the cooling segment, wherein the selection and separation of fragments and dusts of the white slag having a size less than a predetermined size is carried out. The dram is covered with modular panels fixed in a removable manner thereto and it is permeated by a cooling fluid to obtain the indirect cooling of the white slag when placed inside the first segment of the drum.

The Applicant has established that the technical solutions described above are extremely expensive and complex to implement. The main element of known plants is the rotating cylinder (or drum) which, in the event of malfunctions or breakages, given its dimensions, the thermal stresses which it has to undergo and the level of wear caused by the sliding of the material, must be completely revamped to identify any areas of intervention. The possibility also exists of metal parts being introduced into the reactor, thus causing considerable damage to the plant. If on-site repairs are not possible, the entire cylinder must be removed from the plant with enormous time waste and economic losses.

The content of other patent documents relating to cooling treatments and/or material selection is briefly described below.

JPS5515291U describes a plant comprising a refractory hopper inside which the molten slag produced by a blast furnace or by a converter is collected prior to the granulation thereof. The bottom of this hopper is inclined so that the slag is directed towards a pair of rollers with adjustable distance, adapted to“draw” the cooled slag so as to form a slab. Downstream of this pair of drawing rollers there is a slightly inclined plane, made up of a series of rollers internally cooled with water, under which a spray cooling system operates on the still liquid slag which, if necessary, draws through the rollers themselves. The slab thus obtained is finally crushed.

The plant described by JPS5515291U, however, is not suitable for the treatment of white slag because, unlike other types of iron and steel slag (blast furnace, converter, electric furnace), it has the peculiar characteristic of withering during cooling, so it would not allow the formation of a continuous slab according to the teachings of JPS5515291U. Moreover, the plant described by JPS5515291U does not allow any dimensional separation of the material after its granulation. EP2799801A1 describes a device and a method for air cooling of a generic material, with explicit reference to clinker, a granular product. This plant has a fine-grain separation area, where the cooling air passing through the bed of material from below, selectively separates the fine grains towards the upper part of the bed itself, and a subsequent cooling area which is crossed by an air flow rate which is lower than the previous area.

The plant described by EP2799801 Al consists of an inclined chute, of the fixed type, which receives the hot clinker to be cooled and conveys it towards the fine grain separation area. The fine grain separation area and the subsequent cooling area consist of a plurality of moving surfaces which support a series of moving grids arranged in the direction of conveyance of the material.

The plant forming the subject of EP2799801 Al is not, however, suitable for the treatment of white slag which, once withered, would be“volatilized” by the flow of cooling air itself, passing through it from below. Moreover, this plant does not perform any dimensional separation, but is rather adapted to modify the stratification of the bed of material to be cooled, in order to optimize the thermal recovery in the cooling air and reduce the pressure drops of the air during the crossing of the bed itself.

Description of the Invention

In the light of the above-mentioned drawbacks of the technologies available today, whether related to the treatment of white slag (with particular reference to the use of a rotary reactor with indirect exchange) or the treatment of bulk solid materials, although not applicable to the cooling of white slag, the Applicant has developed a solution which is able to speed up the maintenance of the plant and make it more effective by providing an alternative form of the parts adapted to cool and separate the slag, while at the same time maintaining high standards of both quantity and quality level in the white slag recovery process.

The Applicant has intervened by reducing the dimensions of the individual parts designed to cool, convey and separate the slag, thus facilitating the identification of any parts subject to maintenance and speeding up, as a result, repair or replacement operations. This way, the cost of repairs is considerably reduced, thus avoiding long machine downtimes.

The Applicant has also felt the need to create a plant which permits controlling the screening of dust and slag fragments according to the desired grain size in different areas of the plant by applying different systems for indirect heat exchange depending on the cooling needs of the slag.

The present invention therefore relates to a plant for the recovery of the white slag resulting from iron and steel production processes having structural and functional characteristics such as to satisfy the aforementioned requirements and at the same time overcome the drawbacks mentioned with reference to the prior art, by cooling and screening the white slag continuously and simultaneously. This object is achieved by a plant for the recovery of the white slag resulting from iron and steel production processes according to the characteristics of claim 1. Brief Description of the Drawings

Other characteristics and advantages of the plant in accordance with the present invention will be evident from the following description of preferred embodiments thereof, illustrated as an example, but not limited thereto, in the attached tables of drawings in which:

- Figure 1 shows a perspective view of the plant for the recovery of white slag in accordance with the present invention;

- Figure 2 shows a perspective view of the plant of Figure 1 without the supporting framework;

- Figure 3 shows a front perspective view of the cooling ramp for material adduction of the plant of Figure 1 ;

- Figure 4 shows a rear perspective view of the cooling ramp of Figure 3;

- Figure 5 shows a perspective view of the first cooling stage of the plant of Figure 1;

- Figure 6 shows a perspective view of the second cooling stage of the plant of Figure 1;

- Figure 7 shows a detailed perspective view of the cooling elements constituting the second stage of Figure 6;

- Figure 8 shows a perspective view of the plant of Figure 1 wherein some of the blades of the stages have been removed to highlight the further cooling assemblies and the slag recovery channels;

- Figures 9 and 10 show side views of two adjacent rotating cooling members;

- Figure 11 shows a detailed side view of the cooling member of Figure 5;

- Figure 12 shows a perspective view of a further embodiment of the plant in accordance with the present invention.

Embodiments of the Invention

With particular reference to Figure 1, reference numeral 1 globally designates a plant for the recovery of white slag resulting from iron and steel processes in accordance with the present invention.

The plant 1 comprises a loading chute 2 of the white slag with the function of conveying to the plant 1 the white slag received e.g. from a hopper (not shown) located on top of it, a cooling bedplate 3 to screen and feed the slag along a forward direction X-X and first unloading means 4 and second unloading means 5 to recover the white slag fragments and dusts.

The loading chute 2 is developed starting with a plurality of radiating elements 21 which form a cooling panel wherein an upper surface 2a is altogether identified, supporting the white slag, and a lower surface 2b opposite the upper surface 2a. The radiating elements 21 are preferably hollow tubes in which a cooling liquid F, such as e.g. water, can circulate in order to obtain the indirect cooling of the white slag when placed on the upper surface 2a of the chute 2.

As shown in the examples in Figures 3 and 4, the radiating elements 21 are placed side by side and supported by the transverse supporting elements 22,23 which are also hollow and fixed at the lower surface 2b of the chute 2. The radiating elements 21 and the transverse supporting elements 22,23 preferably have a square section and are in fluidic communication with each other to circulate the cooling liquid F between an inlet manifold 23 a, connected to the lower transverse support 23, and an outlet manifold 22a, connected to the upper transverse support 22 of the loading chute 2. The manifolds 22a, 23a are connected to a typical hydraulic cooling liquid circulation circuit (not shown here).

The plant 1 comprises a supporting framework 10 resting or fixed horizontally to the ground and composed of a plurality of uprights joined together to form a substantially parallelepiped structure. The supporting framework 10 acts in turn as a support for a sub-frame 11, this too composed of a plurality of uprights joined together to form a substantially parallelepiped structure but of smaller size than the supporting framework 10 so as to be contained internally in the latter.

The term “substantially” used in this description means less than the dimensional and production tolerances.

As shown in the example in Figure 1, the supporting framework 10 comprises four vertical uprights 101 joined to a plurality of horizontal uprights positioned at different heights to form the lower 102, median 103 and upper 104 supporting planes for the support of the various elements making up the plant 1 , as will be better specified in detail in the rest of the present description. In this case, the lower supporting plane 102 is made up of four horizontal uprights joined together to form a quadrilateral structure from which the vertical uprights 101 project, at the vertices. Similarly, the upper supporting plane 104 is made up of four horizontal uprights to form a quadrilateral structure joined on top of the vertical uprights 101. Preferably, at a median height of the vertical uprights 101 are fixed the four horizontal uprights that make up the median supporting plane 103.

Similarly, the sub-frame 11 is composed of four horizontal uprights to form a quadrilateral structure 110 from which project two vertical uprights 111. The vertical uprights 111 are connected to each other by a cylindrical bar 112 the extremities 112a, 112b of which protrude with respect to the vertical uprights 111 to fit into hinges 12 fixed at the upper extremity of the vertical uprights 101 of the framework 10. This way, the sub-frame 11 can be moved in rotation around the axis of the cylindrical bar 112 and extended along a perpendicular direction Y-Y with respect to the forward direction X-X, according to a plurality of orientations in order to slow down or speed up the forward movement of the white slag. For this purpose, two hydraulic jacks 13 fixed to the uprights of the median supporting plane 103 permit the controlled movement of the sub-frame 11 with respect to the framework 10.

Advantageously, the openings between the uprights of the framework 10 can be closed by one or more panels (not shown) in order to create a hermetic environment with which one or more connections can be associated for the insertion of one or more extraction units in order to permit the extraction and the evacuation of any dust generated in the process of recovery of the white slag.

As shown in the example in Figure 2, downstream of the loading chute 2 there is a cooling bedplate 3 adapted to receive the white slag coming from the loading apparatus 2 and intended to screen and convey, along the forward direction X-X, the fragments and dust of the white slag towards the unloading means 4, 5 according to a predetermined size. The cooling bedplate 3 identifies the cooling path of the white slag between the loading chute 2 and the unloading means 4, 5 and basically acts both as a screening element, and as a movement element for the slag along the longitudinal direction X-X towards the second unloading means 5, as will be explained in detail in the rest of the present description.

The cooling bedplate 3 comprises a plurality of cooling members 310,320 positioned side by side and rotating around their axial direction of extension Y- Y, the latter being perpendicular to the forward direction X-X of the dust.

Advantageously, the cooling bedplate 3 comprises at least a first cooling stage 31 and at least a second cooling stage 32 placed in cascade to the first stage 31. Advantageously, the cooling bedplate 3 is open on top so that the slag conveyed by it is directly facing the inner surface of the upper closing panel (not shown) of the supporting framework 10.

The first cooling stage 31 receives the white slag from the chute 2 to screen it and convey it so that the fragments and dust of the white slag are selected and distributed in the plant 1 according to a predetermined size. As will be seen below, if the white slag fragments and dusts are still greater than the specified size, they are transferred to the second cooling stage 32.

The second stage 32 is therefore adapted to continue the conveying and cooling operations of the material coming from the first stage 31 but with different operating modes, i.e. with a different forward speed and/or by means of different flow rates of the cooling liquid.

Appropriately, both the first stage 31 and the second stage 32 comprise the relevant cooling members 310, 320 which can be operated independently of each other, in such a way that they are able to rotate at different speeds so as to vary the residence time, and therefore the cooling time, of the material on them. On the other hand, if the fragments and dusts of the white slag have a smaller size than the predetermined size, they precipitate towards the first unloading means 4 positioned below the cooling bedplate/path 3 of the plant 1.

In detail, the first cooling stage 31 comprises a plurality of cooling members 310 arranged side by side and intended to rotate around their own axes extended along the direction Y-Y.

According to the invention, each cooling member 310 has a shape, in cross section, substantially elliptical in which opposite and parallel side edges 3l0a,3l0b can be identified. Preferably, the cooling members 310 of the first cooling stage 31 have substantially identical dimensions and shapes.

Conveniently, at their end extremities, each member 310 comprises a pair of support terminals 322 mounted revolving on sides 313 fixed to the sub-frame 11. To one of the support terminals 322 is fixed a cog wheel 314 intended to engage with a corresponding cog wheel of an adjacent member 310 so that the rotation of the members 310 is in agreement with respect to the forward direction X-X which translates into an overall wave motion for the slag which has the purpose of moving the material forward and keeping it as much as possible in contact with the rotating members to facilitate cooling thereof.

In an alternative version, the cog wheels 314 can be engaged by a single kinematic mechanism, e.g., a chain (not shown).

Advantageously, the speed of rotation of the members 310 is variable according to the movement needs of the white slag. For this purpose, mechanical kinematics (not shown) are provided connected to one or more cog wheels 314 to move the cooling members 310 synchronously, e.g., with inverter control. Preferably, both the cooling members 310 and the support terminals 322 are hollow and are in fluid communication with each other to receive a cooling fluid F inside them intended for the indirect cooling of the white slag when supported by the cooling members 310.

Conveniently, the cooling members 310 associated with the first cooling stage 31 have a substantially flat and smooth outer surface.

As shown in the example in Figure 5, the center distance between the various cooling members 310 is set so that during the rotation of the latter, the side edges of two adjacent cooling members 310 are separated from each other according to a preset distance depending on the predetermined size of the fragments and dust which the first cooling stage 31 has to filter in order to obtain an extremely effective screening.

Preferably, the center distance between the cooling members 310 of the first stage 31 is adjustable, in order to vary the distance that separates the relative side edges, so as to vary the dimensions of the predetermined size and/or compensate for any wear due to use. As shown in the example in Figures 3, 5 and 8, below the cooling stage 31 there is a first cooling assembly 7 provided with a plurality of tubes 71 extending along the perpendicular direction Y-Y to receive a cooling fluid F inside these intended for the further indirect cooling of the white slag when precipitating from the first cooling stage 31 and therefore from the cooling members 310. In essence, before reaching the first unloading means 4, the temperature of the white slag fragments and dust further drops by intercepting the tubes 71.

With reference to the examples shown in Figures 6 and 7, downstream of the first cooling stage 31 there is the second cooling stage 32 meant to receive the white slag from the first cooling stage 31 for further screening and for conveying it to the first or second unloading means 5. Preferably, the second cooling stage 32 extends on a lower surface than the extension surface of the first cooling stage 31. Conveniently, between the two cooling stages 31, 32 there is a chute 33 to facilitate the drop of the slag from the first cooling stage 31 to the second cooling stage 32.

In essence, if the fragments and dust of the white slag are greater than the predetermined size received from the first cooling stage 31, they are transferred to the second unloading means 5. Otherwise, if the fragments and dust of the white slag are smaller than the predetermined size received from the first cooling stage 31, they precipitate towards the first unloading means 4 located below the bedplate/cooling path 3 of the plant 1. As can be seen in fact from the attached illustrations, the first unloading means 4 comprise a collection tank 6 which extends substantially along the entire length of the cooling bedplate 3 and therefore below both the first cooling stage 31 and the second cooling stage 32. Preferably, the second unloading means 5 may comprise an unloading vessel for the expulsion or a basket for the collection of the slag from the plant.

In one version, the second unloading means 5 are associated exclusively with the cooling bedplate 3 for the extraction of fragments and dust of white slag having a greater size than the predetermined size.

Similarly to what was described with reference to the first cooling stage 31, the second cooling stage 32 comprises a plurality of cooling members 320 arranged one next to the other and intended to rotate around their own axes extended along the direction Y-Y.

According to the invention, each cooling member 320 has a substantially elliptical shape, in cross section, wherein opposite and parallel side edges 320a, 320b are identified. Preferably, the cooling members 320 of the second cooling stage 32 are substantially identical in size and shape.

Conveniently, at their end extremities, each member 320 comprises a pair of support terminals 322 mounted rotating on sides 323 fixed to the sub-frame 11. To one of the support terminals 322 is fixed a cog wheel 324 intended to engage with a corresponding cog wheel of an adjacent rotating member 320 so that the rotation of the members 320 is identical.

In an alternative version, the cog wheels 324 can be engaged by a single kinematic mechanism, e.g. a chain (not shown), so that the direction of rotation of all the rotating members 320 of the second cooling stage 32 is the same.

Advantageously, the rotational speed of the members 320 is also variable, depending on the movement requirements of the white slag. For this purpose, kinematic mechanisms (not shown) are provided connected to one or more cog wheels 324 to move the rotating members 320 synchronously, e.g. with inverter control.

Appropriately, the rotational speed of the cooling members 310 of the first stage 31 is different from the rotational speed of the cooling members 320 of the second stage 32.

Preferably, both the cooling members 320 and the support terminals 322 are hollow and are in fluidic communication with each other to receive a cooling fluid F inside them for the indirect cooling of the white slag when supported by the cooling members 310.

Conveniently, the rotating members 320 associated with the second cooling stage 32 have a grooved or smooth outer surface.

As explained with reference to the cooling members 310 of the first cooling stage 31, the center distance between the various rotating members 320 of the second cooling stage 32 is also set so that during the rotation of the latter, the side edges of two adjacent rotating members 320 are separated from each other according to a preset distance according to the predetermined size of the fragments and dust which the second cooling stage 32 has to filter. The surfaces of the rotating members 320 can be usefully designed so that these engage at least partly with each other during rotation. Preferably, the center distance of the cooling members 320 of the second stage 32 is adjustable, in order to vary the distance that separates the relative side edges, so as to vary the dimensions of the predetermined size and/or compensate for any wear due to use. It follows that, by appropriately setting the center distance between the rotating members 320, it is possible to determine the space required to screen the white slag and therefore the final dimensions of the withered material.

It should be noted that the number of cooling members 310, 320 is variable according to the desired amount of heat exchange between the slag and the same members, fixed by the quantity and temperature of the slag being fed.

As shown in the example in Figures 6, 7 and 8, below the second cooling stage 32 there is a second cooling assembly 8 provided with a plurality of tubes 81 extending along the perpendicular direction Y-Y to receive a cooling fluid F inside them and intended for the further indirect cooling of the white slag when precipitating from the second cooling stage 32 and therefore from the rotating members 320. In essence, before reaching the first unloading means 4, the temperature of the white slag fragments and dust further decreases by intercepting the tubes 81.

Advantageously, below the collection tank 4 there is a conveyor 9 provided inside with a single or double-helix screw feeder, which enables the filtered slag to be evacuated. Usefully, the screw feeder can have one or more hollow portions to receive a cooling fluid F inside it for the further indirect cooling of the slag.

In a further embodiment not shown, the second cooling stage 32 can be used for screening without cooling by vibration (e.g., by replacing the rotating cooling members with a mesh net of the desired grain size). For this purpose, appropriate motor-driven vibrating means will be associated with the second cooling stage 32 to make it vibrate.

With reference to the examples shown in Figures 10 and 11 and as already mentioned in the present description, each cooling member 310, 320 has a profile with a substantially elliptical section such as to maintain an almost constant distance D between the outer surfaces of the members 310, 320 during the rotation thereof. For simplicity of presentation, we will refer below to the cooling members of the first cooling stage 31. However, the following description regarding the external profile of the cooling members 310 is also valid with reference to the cooling members 320 of the second cooling stage 32. In detail, Figures 9 and 10 show how the particular external profile of the members 310 causes the distance D between the outer surfaces 311,312 to be constant during rotation thereof, in the illustrated example by about 30°, maintaining a substantially identical rotational speed of the adjacent members

310.

For this purpose, the profile of each cooling member 310 of the first cooling stage 31 , as shown in Figure 11 , comprises a pair of first curvilinear surfaces

311, opposite one another, and a pair of second curvilinear surfaces 312 also arranged opposite each other. The surfaces 311, 312 are arranged alternately and contiguous so that the profile of the member 310 is continuous.

The first surfaces 311 correspond to arcs of a circle having a radius n greater than the radius r ₂ of the second surfaces 312. It should be noted that the radius n of each of the first surfaces 311 rotates with respect to a midpoint placed on the opposite surface while the radius r ₂ of each of the second surfaces 312 rotates with respect to the focuses fi, f ₂ of the member 310 indicated in Figure 9.

According to an embodiment not shown, the plant 1, in accordance with the present invention, may comprise a weighing scale designed to indicate, continuously, the flow rate of the white slag conveyed and screened by subtracting such flow rate from the weight of the slag still present in the loading hopper.

In accordance with the embodiment shown in Figure 12, the plant 1 may comprise a plurality of cooling stages 31,32,33, in particular arranged one below the other and preferably inclined. In detail, the first and second cooling stages 31,32 are substantially similar in length and have opposite inclinations, while the third cooling stage 33 has an inclination substantially identical to the inclination of the first cooling stage 31. The cooling stages 31,32,33 are arranged in such a way that the slag is screened and conveyed according to a zigzag path with downward direction, making it possible to save space inasmuch as the plant 1 extends to a greater height. The changes in direction of the slag along the path are possible thanks to the presence of rebound walls 17,18 each positioned at the end of the path of the first cooling stage 31 and second cooling stage 32, respectively, which suitably direct the slag during the drop.

Each cooling stage 31,32,33 can provide for the presence of cooling members 310 with a smooth surface or with a grooved surface 320.

Advantageously, such configuration makes it possible to increase the exchange surface (and therefore to reduce cooling time) since the slag conveyed by the first cooling stage 31 is again conveyed and screened by the second cooling stage 32 and finally conveyed and screened by the third cooling stage 33 towards the first unloading means 4 and the second unloading means 5.

Appropriately, in particular, in the event of the cooling stages 31,32,33 being superimposed on each other, the plant 1 may comprise vibrating means (not visible in detail in the figures) associated with at least one of the cooling stages 31,32,33, adapted to prevent the dust falling from the above stage from settling on the slag to be treated, thereby reducing the thermal conductivity thereof. Such vibrating means are therefore adapted to make the cooling members 310,320 of the relative stage 31,32,33 vibrate.

According to an embodiment not shown, the plant 1 of Figure 12 can comprise cooling assemblies (completely similar to the cooling assemblies 7,8 described above) which can be positioned below at least one of the cooling stages 31,32,33 in order to provide further indirect cooling of the white slag when it precipitates from each of the cooling stages 31,32,33 and therefore from the cooling members 310,320. In one version, the cooling assemblies are positioned below all the cooling stages 31,32,33.

The operation of the present invention is the following.

Initially, a phase is envisaged wherein the slag is introduced into a hopper (not shown) from where the material is conveyed to the previously cooled loading chute 2. The slag is conveyed by the cooling members 310,320 to the loading chute 2 and is monitored by means of appropriate sensors to determine its temperature along the path of forward movement in the plant.

If, at the exit of the first cooling stage 31, the temperature of the slag is not adequate, a reduction phase is envisaged of the rotational speed of the cooling members 310 to improve the thermal exchange between the slag and the rotating members themselves. For example, the detected temperature is sent to a dedicated software which increases or decreases the rotational speed of the cooling members 310,320 in order to enable the slag to exchange heat with the cooling elements of the plant 1 for more or less time.

Optionally, a phase is envisaged wherein the sub-frame 11 is inclined with respect to the framework 10 so that the forward speed of the material along the path is increased.

Part of the fragments and dust of the slag which passes through the first stage 31 is filtered according to its size and precipitates towards the collection tank 4. The slag with a greater size than the predetermined size moves forward and is conveyed to the second cooling stage 32.

The slag is received by the second stage 32 and made to move forward by means of the rotating members 320, depending on its size, towards the collection basket 5. On the other hand, the slag, which is smaller than the predetermined size, precipitates towards the collection tank 4.

Finally, the slag and its relative dust and fragments are expelled from the tank 4 and from the collection basket 5 to be subsequently recovered or disposed of.

As it has been possible to determine from the present description, it has been ascertained that the described invention achieves the intended objects and in particular the fact is underlined that by means of the plant of the invention it is possible to recover dust and fragments of white slag resulting from iron and steel production processes in a fast and effective way and also to be able to reuse it in the same iron and steel production plant.

Moreover, thanks to the particular cooperation between the cooling stages, the rotating members and the other cooling elements making up the plant, the indirect heat exchange is considerably improved in order to reduce the temperature to the slag. Moreover, by means of the presence of appropriate computerized means and relative sensors, it is possible to set all the mutual movements of the rotating members in an automated manner, enabling the plant to work even without the presence of qualified personnel. The embodiments of the system described above are numerous and obviously an expert in the field, in order to satisfy contingent and specific needs, can make changes and variations, all of which in any case contained within the scope of protection of the invention, as defined by the following claims.